As this type of apparatus, an apparatus for performing air-fuel ratio rich control at the time of recovery from the fuel cut control has been suggested (e.g. refer to a patent document 1). According to the air-fuel ratio control apparatus for an internal combustion engine disclosed in the patent document 1, the air-fuel ratio rich control is stopped if standard amount of oxygen released, calculated on the basis of a target rich air-fuel ratio which is not influenced by a detected value of an exhaust air-fuel ratio sensor, is greater than or equal to an upper limit value of the amount of oxygen released. Thus, even if detection accuracy of the exhaust air-fuel ratio sensor is reduced and a detected exhaust air-fuel ratio is shifted to a lean side with respect to an actual exhaust air-fuel ratio, excessive continuation of the air-fuel rich control is considered to be suppressed.
Incidentally, there has been also suggested a control apparatus for a hydrogen engine which suppresses vibration and noise due to abnormal combustion of hydrogen by injecting gasoline before enriching an air-fuel ratio when the air-fuel ratio is enriched in order to release NOx in a bifuel engine which can use the hydrogen and the gasoline (e.g. refer to a patent document 2).